NATURE OF THE LIGHT EMITTED BY FIREEUES. 45 



genie layer and the so-called "reflecting layer" are penetrated by innumer- 

 able tracheae, which are supposed to be filled with air. During the experi- 

 ments recorded herewith, it was found that the fireflies must have access to 

 plenty of fresh air to keep them healthy and active. In fact, to the writer it 

 appeared that they required more fresh air (oxygen) than would be required 

 in the ordinary respiratory processes. Other insects (e. g., several non- 

 luminous Elaters) did not seem so sensitive in this respect. 



While it is generally accepted that the light production is connected in 

 some manner with an oxidation process, there is no data showing how the 

 light emission is brought about. Optically the so-called "reflecting layer " 

 has little if any meaning. Whether it is the storehouse for waste products 

 or (what is more plausible) a reservoir containing an oxidizable substance is 

 a subject deserving further consideration. As mentioned elsewhere, it 

 would be desirable to learn the condition of this layer with the age of the 

 insect, and especially after it has flashed for a long time. Since samples of 

 Photuris can be obtained which will flash in rapid succession for at least i to 

 i| hours, it would be interesting to compare its "reflecting layer" with that 

 of a specimen which has not flashed in this manner. But while this may 

 give some information in regard to the light production in fireflies, it will 

 hardly apply to all organisms. In some organisms the light is developed in 

 a less highly organized cell; and, indeed, in the case of some marine animals 

 a liquid is ejected which becomes luminous on diffusing in the water. In 

 this connection Dubois has already been quoted that the light is produced 

 when the ejected liquid passes from a colloidal into a crystalline state. 

 Ultimately it may perhaps be shown that the light production is the result 

 of energy transformations in passing from the colloidal to the crystalline 

 state. In this connection the optical properties of thermo-luminescent fluo- 

 rites has been the subject of some study by the writer, but no definite 

 results have yet been obtained. Just what happens when fluorite is warmed 

 and the thermo-luminescence destroyed is not known. Whether this has 

 any bearing on the light emission in animals is difficult to determine. 



Washington, D. C, September i, ipii. 



